1. Field of the Invention
The present invention relates to a novel agent for capturing metal ions consisting essentially of a specific cyclic inulooligosaccharide.
2. Discussion of Background
Heretofore, many methods have been proposed for separating and removing metal ions from various compounds or mixtures. As a typical example, there is a method of capturing and recovering metal ions in a solution by means of a chelate compound. Further, a method of recovering metal ions by means of cyclodextrin known to form a clathrate compound, or a method of employing various crown ethers, is also well known.
The method for capturing metal ions by means of a chelate compound had a problem that it was difficult to properly select a chelate compound suitable for the metal ions to be captured, since the capturing performance depends on various factors including the types of the metal ion and the ligand forming the chelate compound and the size of the chelate ring.
In the case of the capturing and recovering method by means of cyclodextrin, cyclodextrin has in its molecule a hydrophobic space by virtue of its specific molecular structure and takes into the space various compounds in an aqueous solution to form a clathrate compound, whereby guest molecules having higher hydrophobic nature tend to be more readily taken into the space. Accordingly, there has been a problem that ions having low hydrophobic nature can not be captured by such cyclodextrin. Further, there has been a problem that cyclodextrin is hardly soluble in water.
The method of employing crown ethers has problems such that crown ethers are insoluble in water, and they are highly toxic to human bodies.
Further, these conventional metal ion capturing agents are all expensive, and their applicable ranges are rather limited.